Carbonaceous material for hydrogen storage and method for preparation thereof, carbonaceous material having hydrogen absorbed therein and method for preparation thereof, cell and fuel cell using carbonaceous material having hydrogen absorbed therein

ABSTRACT

A hydrogen-storing carbonaceous material is provided. The hydrogen-storing carbonaceous material is obtained by heating a carbonaceous material at lower than about 800° C. before hydrogen is stored under the pressure of hydrogen of about 50 atmospheric pressure or higher. The present invention also provides hydrogen-stored carbonaceous material that is obtained by hydrogen storage in the hydrogen-storing carbonaceous material under the pressure of hydrogen of about 50 atmospheric pressure or higher. This hydrogen-stored carbonaceous material is used for a battery or a fuel cell. The hydrogen-stored carbonaceous material is heated at lower than about 800° C. before the hydrogen is stored under the pressure of hydrogen of about 50 atmospheric pressure or higher, so that the hydrogen-storing carbonaceous material whose hydrogen storage capacity is greatly enhanced can be produced.

RELATED APPLICATION DATA

The present application claims priority to Japanese Patent ApplicationNo. P2000-074432 filed on Mar. 16, 2000, herein incorporated byreference to the extent permitted by law.

BACKGROUND OF THE INVENTION

The present invention relates to a hydrogen-storing carbonaceousmaterial and a method for producing it, a hydrogen-stored carbonaceousmaterial and a method for producing it and a battery and a fuel cellusing a hydrogen-stored carbonaceous material, and more particularly toa hydrogen-storing carbonaceous material and a method for producing it,a hydrogen-stored carbonaceous material and a method for producing itand a battery using the carbonaceous-stored carbonaceous material and afuel cell using the hydrogen-stored carbonaceous material.

Fossil fuel such as gasoline, light oil, or the like have and continueto be widely used as the energy source for producing an electric poweras well as the energy source of motor vehicles or the like. The fossilfuel not only may possibly degrade a global environment, but also isexhaustible and questionable whether or not the fossil fuel can bestably supplied.

Hydrogen has been paid attention to in place of the fossil fuel havingthe above described possibilities. The hydrogen is contained in water,inexhaustibly exists on the earth and includes a large quantity ofchemical energy per amount of material. Further, the hydrogen hasadvantages as a clean and inexhaustible energy source by which thefossil fuel is replaced, because the hydrogen does not discharge harmfulsubstances or global greenhouse gas or the like when it is used as theenergy source.

Especially recently, the fuel cell that an electric energy can begenerated from the hydrogen energy has been eagerly studied anddeveloped and it has been expected that the fuel cell is applied to alarge-scale power generation, an onsite private power generation, andfurther, to a power supply for a motor vehicle.

On the other hand, since the hydrogen is gaseous under ambienttemperature and ambient pressure, it is treated with more difficultythan liquid or solid. Since the density of the gas is extremely small ascompared with that of liquid or solid, the chemical energy of the gas issmall per volume. Further, it is inconveniently difficult to store ortransport the gas. Still further, since the hydrogen is gas, it isliable to leak. When the hydrogen leaks, the danger of explosion isundesirably generated, which is problematic with respect to theutilization of the hydrogen energy.

Thus, in order to put an energy system using the hydrogen energy topractical use, the development of a technique that the gaseous hydrogenis efficiently and safely stored in a small volume has been promoted.There have been proposed a method for hydrogen storage as high pressuregas, a method for hydrogen storage as liquefied hydrogen and a methodfor using a hydrogen-storing material, or the like.

In the method for hydrogen storage as the high pressure gas, since avery strong metallic pressure proof vessel such as a cylinder needs tobe used as a storage vessel, the vessel itself becomes extremely heavyand the density of the high pressure gas is ordinarily about 12 mg/cc.Accordingly, not only the storage density of the hydrogen isdisadvantageously terribly small and a storage efficiency is low, butalso there has a problem in view of safety because of high pressure.

On the contrary, in the method for hydrogen storage as the liquefiedhydrogen, the storage density is ordinarily about 70 mg/cc. Although thestorage density is considerably high, it is necessary to cool hydrogendown to lower than −250° C. in order to liquefy, so that an additionaldevice such as a cooling device is required. Therefore, not only asystem has been undesirably complicated, but also energy for cooling hasbeen needed.

Further, hydrogen-stored alloys are most effective materials among thehydrogen-stored materials. For instance, there have been knownlanthanum-nickel, vanadium, and magnesium hydrogen-stored alloys. Thepractical hydrogen storage density of these hydrogen-stored alloys isgenerally 100 mg/cc. Although the hydrogen is stored in thesehydrogen-stored alloys, the hydrogen storage density of these alloys isnot lower than that of liquefied hydrogen. Therefore, the use of thehydrogen-storing materials is the most efficient among conventionalhydrogen storage methods. Further, when the hydrogen-storing alloy isused, the hydrogen can be stored in the hydrogen-storing alloy and thehydrogen can be discharged from the hydrogen-storing alloy at aroundroom temperature. Further, since the hydrogen storage condition iscontrolled under the balance of the partial pressure of hydrogen, thehydrogen-storing alloy is advantageously treated more easily than thehigh pressure gas or the liquefied hydrogen.

However, since the hydrogen-stored alloys consist of metallic alloys,they are heavy and the amount of stored hydrogen is limited toapproximately 20 mg/g per unit weight, which may not be said to besufficient. Further, since the structure of the hydrogen-storing alloyis gradually destroyed in accordance with the repeated the cycle ofstoring and discharging of hydrogen gas, a performance is undesirablydeteriorated. Still further, there may be possibly generated fears ofthe problems of resources and an environment depending on thecomposition of the alloy.

Thus, for overcoming the above described issues of the conventionalmethods for hydrogen storage, a carbon material is paid attention to asthe hydrogen-storing material.

For example, Japanese Patent Application Laid-Open No. hei. 5-270801proposes a method that the addition reaction of hydrogen is applied tofullerene to store hydrogen. In this method, since a chemical bond suchas a covalent bond is formed between a carbon atom and a hydrogen atom,this method is to be called an addition of hydrogen rather than ahydrogen storage. Since the upper limit of the amount of hydrogen whichcan be added by the chemical bonds is essentially restricted to thenumber of unsaturated bonds of carbon atoms, the amount of storedhydrogen is limited.

Further, Japanese Patent Application Laid-Open No. hei. 10-72201proposes a technique that fullerene is used as the hydrogen-storingmaterial and the surface of the fullerene is covered with catalyticmetal such as platinum deposited by a vacuum method or a sputteringmethod to store hydrogen. In order to employ platinum as the catalyticmetal and cover the surface of fullerene with it, much platinum needs tobe used so that not only a cost is increased, but also a problem isgenerated in view of resources.

Known methods for hydrogen storage known are problematic from apractical standpoint when hydrogen energy is utilized. Especially, whenthe hydrogen energy is employed as an energy source for motor vehicles,marine vessels, general domestic power supplies, various kinds of smallelectric devices, or the like or when a large amount of hydrogen needsto be conveyed, the conventional methods for hydrogen storage is notpractical.

SUMMARY OF THE INVENTION

It is an advantage of the present invention to provide ahydrogen-storing carbonaceous material and a method for producing it, ahydrogen-stored carbonaceous material and a method for producing it anda battery and a fuel cell using a hydrogen-stored carbonaceous materialwhich are light-weight, can be repeatedly used in a safe manner and hasminimal, if any, impacts with respect to resource and environmentalissues.

The inventors of the present invention have found that chemisorbed orphysisorbed molecules on the surface of the carbonaceous material wasproblematic hydrogen was stored in the carbonaceous material, however,when the hydrogen was stored under the pressure of hydrogen not lowerthan 50 atmospheric pressure, the carbonaceous material was heated at aprescribed temperature before the hydrogen was storage capability of thecarbonaceous material was greatly enhanced. The present inventionrelates to a hydrogen-storing carbonaceous material obtained by heatingthe carbonaceous material at a temperature lower than 800° C. before thehydrogen is stored under the pressure of hydrogen not lower than 50atmospheric pressure.

According to the present invention in an embodiment, since thecarbonaceous material is effectively heated at lower than 800° C. beforethe hydrogen is stored, so that the hydrogen-storing carbonaceousmaterial whose hydrogen storage capacity is effectively enhanced can beproduced, this results in a light-weight hydrogen-storing carbonaceousmaterial which can efficiently store a large amount of hydrogen, can berepeatedly used in a safe manner, and may not possibly generate problemsfrom the viewpoints of resources and environment.

Further, the present invention in an embodiment relates to a method forproducing a hydrogen-storing carbonaceous material obtained by heatingthe carbonaceous material at not higher than about 800° C. beforehydrogen is stored under the pressure of hydrogen not lower than about50 atmospheric pressure and a hydrogen-stored carbonaceous material inwhich the hydrogen is stored obtained by the method.

According to the present invention, since the carbonaceous material iseffectively simply heated at lower than about 800° C. to store hydrogenunder the pressure of hydrogen of about 50 atmospheric pressure orhigher so that a hydrogen-stored carbonaceous material in which a largeamount of hydrogen is stored can be produced, there can be obtained ahydrogen-storing carbonaceous material which can efficiently store alarge amount of hydrogen, is light-weight, can be repeatedly employed ina safe manner and may not possibly generate problems in view ofresources and an environment.

Still further, the present invention in an embodiment relates to amethod for producing a hydrogen-stored carbonaceous material obtained insuch a manner that the carbonaceous material is heated at lower thanabout 800° C. to store hydrogen under the pressure of hydrogen not lowerthan about 50 atmospheric pressure.

Further, the present invention in an embodiment relates to a batteryhaving an anode, a cathode, an electrolyte interposed therebetween, andthe anode and/or the cathode includes a hydrogen-stored carbonaceousmaterial obtained by heating the carbonaceous material at lower thanabout 800° C. to store the hydrogen under the pressure of hydrogen notlower than about 50 atmospheric pressure.

In an alkaline storage battery in which aqueous alkaline solution suchas potassium hydroxide solution is employed for the electrolyteaccording to an embodiment of the present invention, a proton moves tothe anode from the cathode through the aqueous alkaline solution tostore the proton in the anode during a charging process. The proton canbe moved to the cathode side from the anode side through the aqueousalkaline solution during a discharging process. Further, in ahydrogen-air fuel cell of the invention in which perfluorosulfonic acidpolymer electrolyte film or the like is used for the electrolyte, aproton previously stored in a hydrogen electrode by a charging orstoring process is supplied to an air electrode through the polymerelectrolyte film during the discharging process. Accordingly, in thebattery according to the present invention, an electric power can bestably taken out.

Further, the present invention in an embodiment provides a fuel cellincluding a laminated structure having an anode, a proton conductor anda cathode, a hydrogen storage part including a hydrogen-storedcarbonaceous material obtained by heating a carbonaceous material atlower than about 800° C. to store hydrogen under the pressure ofhydrogen not lower than about 50 atmospheric pressure, discharging thehydrogen and supplying it to the anode.

Since the fuel cell according to an embodiment the present invention hasthe laminated structure of the anode, the proton conductor and thecathode, and the hydrogen storage part including the hydrogen-storedcarbonaceous material obtained by heating the carbonaceous material atlower than about 800° C. to store hydrogen under the pressure ofhydrogen not lower than about 50 atmospheric pressure, discharging thehydrogen and supplying it to the anode, the hydrogen discharged from thehydrogen storage part produces a proton in accordance with a catalyticaction in the anode. The produced proton moves to the cathode togetherwith a proton produced by the proton conductor so that the protonscombine with oxygen to produce water and generate an electromotiveforce. Therefore, the fuel cell according to an embodiment the presentinvention can supply the hydrogen more efficiently than a case in whichthe hydrogen storage part is not provided and can improve theconductivity of the proton.

In the present invention in an embodiment, the hydrogen stored in thecarbonaceous material includes hydrogen molecules, hydrogen atoms, aproton as the atomic nucleus of the hydrogen, the like or mixturesthereof.

In the present invention, in an embodiment, the carbonaceous material ispreferably heated at a temperature ranging from about 100° C. to about800° C. Further, the carbonaceous material is preferably heated underthe atmosphere of inert gas. The inert gas employed is composed of inertgas including nitrogen gas, helium gas, neon gas, argon gas, kryptongas, xenon gas, radon gas or mixtures thereof.

As the carbonaceous material employed in the present invention in anembodiment, a material having a large surface and structural curvatureis selected. The carbonaceous material is composed of a carbonaceousmaterial including fullerene, carbon nanofiber, carbon nanotube, carbonsoot, nanocapsule, bucky onion, carbon fiber or mixtures thereof. As thefullerene, any spheroidal carbon molecules may be used and allspheroidal carbon molecules having the number of carbons such as 36, 60,70, 72, 74, 76, 78, 80, 82, 84, the like or combination thereof can beutilized.

Further, the carbonaceous material used in the present invention in anembodiment includes on its surface fine particles made of metal or ametallic alloy having a function for separating hydrogen atoms fromhydrogen molecules, or further, separating protons and electrons fromthe hydrogen atoms. The average size of the fine particles made of themetal or the alloy is desirably 1 micron or smaller. As the metal, thereis preferably employed metal or an alloy including iron, rare earthelements, nickel, cobalt, palladium, rhodium, platinum or alloyscomposed of one or two or more of these metals the like or combinationthereof.

When the carbonaceous material having the curvature of fullerene, carbonnanofiber, carbon nanotube, carbon soot, nanocapsule, bucky onion andcarbon fiber or the like is produced by an arc discharge method, themetal or the alloy thereof is preferably mixed into a graphite rodbefore the arc discharge. At the time of the arc discharge, the abovedescribed metals or the alloys thereof are allowed to exist, the yieldof the carbonaceous material can be enhanced and the hydrogen-storingcarbonaceous material with the curvature can be urged to be produced inaccordance with the catalytic action of these metals or the alloythereof. It has been known that these metals or the alloys thereofperform a catalytic action when the carbonaceous material such asfullerene, carbon nanofiber, carbon nanotube and carbon fiber or thelike is produced by a laser ablation method. The carbonaceous materialsuch as fullerene, carbon nanofiber, carbon nanotube and carbon fiber orthe like may be collected, added to and mixed with the hydrogen-storingcarbonaceous material so that the surface of the hydrogen-storingcarbonaceous material includes these metals or the alloys thereof.

Further, in the present invention, the carbonaceous material includingthese metals or alloys thereof or the carbonaceous material including nometal or no alloy carries at least on its surface metallic fineparticles of about 10 wt % or less which have a catalyzing function forseparating hydrogen atoms from hydrogen molecules, and further,separating protons and electrons from the hydrogen atoms. In anembodiment, a preferable metal having such a catalyzing function, forexample, platinum or a platinum alloy or the like. In order to carrythese metals on the surface of the carbonaceous material, a well-knownmethod such as a sputtering method, a vacuum deposition method, achemical method, a mixture or the like may be used.

Further, when platinum fine particles or platinum alloy fine particlesare deposited on the carbonaceous material, a method using solutioncontaining platinum complexes or an arc discharge method usingelectrodes including platinum may be applied thereto. In an embodiment,chloroplatinic acid solution is treated with sodium hydrogen sulfite orhydrogen peroxide, then, the carbonaceous material is added to theresultant solution and the solution is agitated so that the platinumfine particles or the platinum alloy fine particles can be carried onthe carbonaceous materials. On the other hand, in the arc dischargemethod in an embodiment, the platinum or the platinum alloy is partlyattached to the electrode part of the arc discharge, and is subjected tothe arc discharge to be evaporated so that the platinum or the platinumalloy can be adhered to the carbonaceous material housed in a chamber.

The above described metals or the alloys thereof are carried on thecarbonaceous material, so that the hydrogen storage capacity can be moreimproved than that when the metals or the alloys thereof are not carriedon the carbonaceous material. Further, it is found that fluorine ormolecule thereof serving as an electron donor or an amine molecule suchas ammonia is mixed or combined with the carbonaceous material toefficiently generate a charge separation.

As described above, hydrogen composed of protons and electrons issupplied to the hydrogen-storing carbonaceous material as a strongelectron acceptor on which the above mentioned metals or the alloys aremounted, hence the hydrogen is stored in the form of protons. Therefore,its occupied volume is greatly reduced and a large amount of hydrogencan be stored in the hydrogen-storing carbonaceous material as comparedwith the storage by the conventional chemisorption of hydrogen atoms.That is, the hydrogen is separated into electrons and protons from thestate of atoms, and the electrons are efficiently stored in thehydrogen-storing carbonaceous material so that a large amount of highdensity hydrogen can be finally stored in the state of protons.Accordingly, when the above described metals or the alloys are carriedon the surface of the hydrogen-storing carbonaceous material, thehydrogen can be more efficiently stored and a larger amount of hydrogencan be stored. The above described hydrogen-storing carbonaceousmaterial is light-weight, easily transported, can be repeatedly employedat around room temperature without generating a structural destructionand can be safely handled. Further, the amount of use of a metalliccatalyst such as platinum can be reduced. The carbonaceous material suchas fullerene serving as a starting material can be also produced at alow cost. Further, the materials associated with the present inventionare virtually in unlimited supply and have minimal, if any, impact onthe environment during a use.

Additional features and advantages of the present invention aredescribed in, and will be apparent from the following DetailedDescription of the invention and figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing a schematic structure of a fuel cellaccording to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic structure of an alkaline storagebattery (secondary battery) according to an embodiment of the presentinvention.

FIG. 3 is a graph showing the cyclic characteristics of the alkalinestorage battery according to an embodiment of the present invention.

FIG. 4 is a diagram showing a schematic structure of a hydrogen-air fuelcell according to an embodiment of the present invention.

FIG. 5 is a graph showing the discharge characteristics of thehydrogen-air fuel cell according to an embodiment of the presentinvention.

FIG. 6 is a graph showing the discharge characteristics of an anotherhydrogen-air fuel cell according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The fuel cell according to an embodiment of the present invention isprovided with a cathode 1 and an anode 2 arranged so as to be opposed toeach other as shown in FIG. 1. Here, as the cathode 1, an oxygenelectrode is used. As the anode 2, a fuel electrode or a hydrogenelectrode is used. The cathode 1 has a cathode lead 3 and a catalyst 5is dispersed in the cathode or is adhered to the cathode. The anode 2also has an anode lead 6 and a catalyst 7 is dispersed in the anode oris adhered to the anode. A proton conductor 8 is sandwiched in betweenthe cathode 1 and the anode 2. Hydrogen 12 as fuel is supplied to apassage 13 in the side of the anode 2 through an introducing port 11from a hydrogen supply source 10, and discharged from a discharge port14. In the side of the cathode 1, air 15 is supplied to a passage 17from an introducing port 16 and discharged from a discharge port 18.

While the hydrogen 12 serving as the fuel supplied to the passage 13from the introducing port 11 passes the passage 13, protons aregenerated and the generated protons move to the side of the cathode 1together with protons generated in the proton conductor 8. As a result,the protons react with oxygen in the air 15 supplied to the passage 17from the introducing port 16 and directed to the discharge port 18 sothat a desired electromotive force is generated.

In the present invention in an embodiment, for the hydrogen supplysource 10, is employed a hydrogen-stored carbonaceous material obtainedby heating a carbonaceous material such as fullerene, carbon nanofiber,carbon nanotube, carbon soot, nanocapsule, bucky onion and carbon fiberor the like at the from about 100° C. to 800° C. under the atmosphere ofnitrogen gas and then storing hydrogen under the pressure of hydrogen ofabout 100 atmospheric pressure or lower.

In the fuel cell according to the present invention in an embodiment,since, while the protons are dissociated, the protons supplied from theanode 2 side move to the cathode 1 side in the proton conductor 8, theconductivity of the protons is characteristically improved. Therefore,since a humidifier which has been typically required for conductingprotons is not needed, a system can be simplified and light-weight.

Without limitation, examples and comparative examples illustrating theeffectiveness of the present invention is described below.

EXAMPLE 1

A carbon nanofiber with one nanotube fiber whose diameter is about 200mm is manufactured by a CVD method and impurities such as a catalystwere effectively removed until purity became 95% or higher before athermobalance measurement was carried out.

The carbon nanofiber of 14.3 mg thus obtained was accommodated in asample cup in a thermobalance and the sample cup including the carbonnanofiber was set in a thermogravimetry apparatus so that the contentsof the thermogravimetry vessel were effectively replaced by usingnitrogen gas.

Then, the carbon nanofiber was heated at 400° C. for 6 hours in theatmosphere of nitrogen gas of 1 atmospheric pressure to prepare ahydrogen-storing carbonaceous material #1.

Subsequently, the hydrogen-storing carbonaceous material #1 thusprepared was not exposed to air and was accommodated in a sample chamberand hydrogen of 50 atmospheric pressure was introduced thereinto. Afterthe hydrogen-storing carbonaceous material was left for one day, thechange of the mass of the hydrogen-storing carbonaceous material #1 wasmeasured.

As a consequence, it was found that the amount of stored hydrogen was4.2 wt % based on an increase of the mass. It should be appreciated thatthe amount of stored hydrogen is a value obtained by dividing the massof stored hydrogen by the mass of carbon.

When the carbon nanofiber was heated respectively in the atmosphere ofhelium gas, in the atmosphere of argon gas, and in the atmosphere ofxenon gas in place of the atmosphere of nitrogen gas to measure theamount of stored hydrogen in the effectively same manner, the sameresult as that when the heating process was carried out in theatmosphere of nitrogen gas was obtained.

EXAMPLE 2

A carbon nanofiber with one nanotube fiber whose diameter is about 200mm was manufactured by a CVD method and impurities such as a catalystwere effectively removed until purity became 95% or higher before athermobalance measurement was carried out.

The carbon nanofiber of 14.3 mg thus obtained was accommodated in asample cup in a thermobalance and the sample cup including the carbonnanofiber was set in a thermogravimetry apparatus so that the contentsof the thermogravimetry vessel were completely replaced by usingnitrogen gas.

Then, the carbon nanofiber was heated at 800° C. for 6 hours in theatmosphere of nitrogen gas of 1 atmospheric pressure to prepare ahydrogen-storing carbonaceous material #2.

Subsequently, the hydrogen-storing carbonaceous material #2 thusprepared was not exposed to air and was accommodated in a sample chamberand hydrogen of 50 atmospheric pressure was introduced thereinto. Afterthe hydrogen-storing carbonaceous material was left for one day, thechange of the mass of the hydrogen-storing carbonaceous material #2 wasmeasured.

As a consequence, it was found that the amount of stored hydrogen was18.9 wt % from the increase of the mass. It is noted that the amount ofstored hydrogen is a value obtained by dividing the mass of storedhydrogen by the mass of carbon.

When the carbon nanofiber was heated respectively in the atmosphere ofhelium gas, in the atmosphere of argon gas, and in the atmosphere ofxenon gas in place of the atmosphere of nitrogen gas to measure theamount of stored hydrogen in the effectively same manner, the sameresult as that when the heating process was carried out in theatmosphere of nitrogen gas was obtained.

EXAMPLE 3

A carbon nanofiber with one nanotube fiber whose diameter is about 200mm was manufactured by a CVD method and impurities such as a catalystwere completely removed until purity became 95% or higher before athermobalance measurement was carried out.

The carbon nanofiber of 14.3 mg thus obtained was accommodated in asample cup in a thermobalance and the sample cup including the carbonnanofiber was set in a thermogravimetry apparatus so that the contentsof the thermogravimetry vessel were completely replaced by usingnitrogen gas.

Then, the carbon nanofiber was heated at 400° C. for 6 hours in theatmosphere of nitrogen gas of 1 atmospheric pressure to prepare ahydrogen-storing carbonaceous material #3.

Subsequently, the hydrogen-storing carbonaceous material #3 thusprepared was not exposed to air and was accommodated in a sample chamberand hydrogen of 100 atmospheric pressure was introduced thereinto. Afterthe hydrogen-storing carbonaceous material was left for one day, thechange of the mass of the hydrogen-storing carbonaceous material #3 wasmeasured.

As a consequence, it was found that the amount of stored hydrogen was5.4 wt % from the increase of the mass. Here, the amount of storedhydrogen is a value obtained by dividing the mass of stored hydrogen bythe mass of carbon.

When the carbon nanofiber was heated respectively in the atmosphere ofhelium gas, in the atmosphere of argon gas, and in the atmosphere ofxenon gas in place of the atmosphere of nitrogen gas to measure theamount of stored hydrogen in the absolutely same manner, the same resultas that when the heating process was carried out in the atmosphere ofnitrogen gas was obtained.

EXAMPLE 4

A carbon nanofiber with one nanotube fiber whose diameter is about 200mm was manufactured by a CVD method and impurities such as a catalystwere completely removed until purity became 95% or higher before athermobalance measurement was carried out.

The carbon nanofiber of 14.3 mg thus obtained was accommodated in asample cup in a thermobalance and the sample cup including the carbonnanofiber was set in a thermogravimetry apparatus so that the contentsof the thermogravimetry vessel were effectively replaced by usingnitrogen gas.

Then, the carbon nanofiber was heated at 800° C. for 6 hours in theatmosphere of nitrogen gas of 1 atmospheric pressure to prepare ahydrogen-storing carbonaceous material #4.

Subsequently, the hydrogen-storing carbonaceous material #4 thusprepared was not exposed to air and was accommodated in a sample chamberand hydrogen of 50 atmospheric pressure was introduced thereinto. Afterthe hydrogen-storing carbonaceous material was left for one day, thechange of the mass of the hydrogen-storing carbonaceous material #4 wasmeasured.

As a consequence, it was found that the amount of stored hydrogen was25.4 wt % from the increase of the mass. Here, the amount of storedhydrogen is a value obtained by dividing the mass of stored hydrogen bythe mass of carbon.

When the carbon nanofiber was heated respectively in the atmosphere ofhelium gas, in the atmosphere of argon gas, and in the atmosphere ofxenon gas in place of the atmosphere of nitrogen gas to measure theamount of stored hydrogen in the absolutely same manner, the same resultas that when the heating process was carried out in the atmosphere ofnitrogen gas was obtained.

When the hydrogen-storing carbonaceous materials #1 to #4 according tothe Examples of the present invention obtained by heating the carbonnanofiber as the carbonaceous material at 400° C. or 800° C. under theatmosphere of inert gas in the above Examples were disposed underhydrogen gas of 50 atmospheric pressure or hydrogen gas of 100atmospheric pressure, it was found that they exhibited an extremely highhydrogen storage capacity.

EXAMPLE 5

An alkaline storage battery was manufactured in the following manner.

Manufacture of Cathode

Carboxymethyl cellulose of 3 wt % was added to spherical nickelhydroxide of 10 g with the average particle size of 30 mm and cobalthydroxide of 1 g and the mixture was kneaded with water to preparepaste. A porous nickel foam with the porosity of 95% was filled with thepaste, and the porous nickel foam filled with the paste was dried andpressed, and then punched to manufacture a cathode having the diameterof 20 mm and the thickness of 0.7 mm.

Manufacture of Anode

The hydrogen-storing carbonaceous material #4 was prepared in accordancewith the Example 4. Carboxymethyl cellulose of 5% and water were addedto the hydrogen-stored carbonaceous material which stored hydrogen underthe pressure of hydrogen of 100 atmospheric pressure in accordance withthe Example 4 to prepare kneaded paste. The porous nickel foam with theporosity of 95% was filled with the paste, the porous nickel foam filledwith the paste was dried and pressed, and then punched to manufacture ananode with the diameter of 20 mm and the thickness of 0.5 mm.

Alkaline Storage Battery

Then, an alkaline storage battery (secondary battery) schematicallyshown in FIG. 2 was manufactured by using the cathode and the anodemanufactured as described above and potassium hydroxide solution of 7Nas electrolyte solution.

The alkaline storage battery comprises a cathode 1, an anode 2 andelectrolyte solution 21 contained therebetween in a battery vessel 20. Acathode lead 3 and an anode lead 6 are taken outside the battery vessel20 from the respective electrodes.

Charge and Discharge Performance

For the alkaline storage battery manufactured as described above, thecharge and discharge test was carried out with 0.1 C, the upper limit of1.4V and the lower limit of 0.8 V. The cyclic characteristics at thattime are shown in FIG. 3.

As apparent from FIG. 3, although it could not be said that a cycle lifewas not sufficient from the viewpoint of structure of the battery, abasic charge and discharge performance could be recognized.

EXAMPLE 6

A hydrogen-air fuel cell was manufactured in the following manner.

Manufacture of Air Electrode

The hydrogen-storing carbonaceous material #2 was prepared in accordancewith the Example 2 and hydrogen was stored under the pressure ofhydrogen of 100 atmospheric pressure in accordance with the Example 2 toobtain the hydrogen-stored carbonaceous material. The hydrogen-storedcarbonaceous material and polymer electrolyte alcoholic solutioncomposed of perfluorosulfonic acid were dispersed in n-butyl acetate toprepare catalyst layer slurry.

On the other hand, a carbon nonwoven fabric with the thickness of 250 mmwas immersed in the emulsion of fluorine water repellent, dried and thenheated at 400° C., so that the carbon nonwoven fabric was subjected to awater repellent process. Subsequently, the carbon nonwoven fabric wascut to the size of 4 cm×4 cm and the catalyst layer slurry prepared asdescribed above was applied to one surface thereof.

Adhesion of Air Electrode to Polymer Electrolyte Film

A polymer electrolyte film composed of perfluorosulfonic acid with thethickness of 50 mm was adhered to the surface of the carbon nonwovenfabric to which the catalyst layer was applied, and then, the filmadhered to the nonwoven fabric was dried.

Manufacture of Hydrogen Electrode

Carboxymethyl cellulose of 5% and water were added to the samehydrogen-stored carbonaceous material as that used for manufacturing theair electrode to prepare paste. A porous nickel foam with the porosityof 95% was filled with the paste, dried and pressed and the dried andpressed porous nickel foam was cut to the size of 4 cm×4 cm tomanufacture a hydrogen electrode with the thickness of 0.5 mm.

Manufacture of Hydrogen-Air Fuel Cell

The hydrogen electrode was superposed on the adhered body of the airelectrode and the perfluorosulfonic acid polymer electrolyte filmobtained as described above by holding the polymer electrolyte filmtherebetween. Both the surfaces thereof were firmly held by Teflonplates with the thickness of 3 mm and fixed by bolts. Many holes withdiameter of 1.5 mm are previously opened on the Teflon plate arranged inthe air electrode side so that air can be smoothly supplied to anelectrode.

The schematic structure of the hydrogen-air fuel cell thus assembled isshown in FIG. 4.

As shown in FIG. 4, in the hydrogen-air fuel cell thus manufactured, ahydrogen electrode 31 and an air electrode 32 are arranged so as to beopposed to each other by locating a polymer electrolyte film 30 betweenthe hydrogen electrode and the air electrode. The outer side of thesemembers is held by a Teflon plate 33 and a Teflon plate 35 provided withmany air holes 34 and all the body is fixed by means of bolts 36 and 36.A hydrogen electrode lead 37 and an air electrode lead 38 arerespectively taken out from the respective electrodes.

Discharge Characteristics of Hydrogen-Air Fuel Cell

Then, the discharge characteristics of the hydrogen-air fuel cell wasexamined.

Initially, electric current was supplied in a charging direction withthe current density of 1 mA/cm² to store hydrogen in the hydrogenelectrode. Then, a discharging operation was carried out with thecurrent density of 1 mA/cm². As a result, the discharge characteristicsas shown in FIG. 5 could be obtained and a function as the hydrogen-airfuel cell was recognized.

Further, before the fuel cell was assembled, hydrogen was previouslystored in the hydrogen electrode under the pressure of 100 kg/cm². Thehydrogen electrode thus stored with hydrogen was superposed on theadhered body of the air electrode and the perfluorosulfonic acid polymerelectrolyte film obtained as described above to assemble thehydrogen-air fuel cell. When the discharge characteristic of theobtained fuel cell was measured with the current density of 1 mA/cm²,the discharge characteristic as shown in FIG. 6 was obtained and afunction as the hydrogen-air fuel cell could be also recognized in thiscase.

It is to be understood that the present invention is not limited to theabove described embodiments and Examples and can include any number ofsuitable modifications thereof. For example, in the above describedembodiments, although the fuel cell using the hydrogen-storingcarbonaceous material and the hydrogen-stored carbonaceous material wasdescribed, the hydrogen-storing carbonaceous material and thehydrogen-stored carbonaceous material according to the present inventionare not limited to the fuel cell but also may be widely applied to usesfor hydrogen storage as well as other batteries such as an alkalinestorage battery, a hydrogen-air fuel cell, or the like.

According to the present invention, there can be provided ahydrogen-storing carbonaceous material which can efficiently store alarge amount of hydrogen, is light-weight, can be repeatedly used in asafe manner and is virtually unlimited in supply with minimal, if any,impacts on the environment and a method for producing it, ahydrogen-stored carbonaceous material and a method for producing it, abattery using a hydrogen-stored carbonaceous material and a fuel cellusing a hydrogen-stored carbonaceous material.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A method of producing a hydrogen-storing carbonaceous material, themethod comprising annealing a carbonaceous material under an atmosphereof an inert gas at a temperature ranging from about 100° C. to about800° C. and subsequently storing hydrogen on the carbonaceous materialunder pressure of hydrogen of about 50 atmospheric pressure or higher.2. The method according to claim 1, wherein the inert gas is selectedfrom a group consisting of nitrogen gas, helium gas, neon gas, argongas, krypton gas, xenon gas, radon gas and mixtures thereof.
 3. Themethod according to claim 1, wherein the carbonaceous material has alarge surface and a structural curvature.
 4. The method according toclaim 3, wherein the carbonaceous material is selected from a groupconsisting of fullerene, carbon nanofiber, carbon nanotube, carbon soot,nanocapsule, bucky onion, carbon fiber and mixtures thereof.
 5. A methodof producing a hydrogen-stored carbonaceous material, the methodcomprising producing a carbon nanofiber material by chemical vapordeposition, annealing under an atmosphere of an inert gas the carbonnanofiber material at a temperature ranging from about 100° C. to about800° C., and storing hydrogen under pressure of hydrogen of about 50atmospheric pressure or higher.
 6. The method according to claim 5,wherein the inert gas is selected from a group consisting of nitrogengas, helium gas, neon gas, argon gas, krypton gas, xenon gas, radon gasand combinations thereof.
 7. The method according to claim 5, whereinthe carbon nanofiber material has a large surface and a structuralcurvature.